Asset Store window is getting blank after docking and undocking twice.

Steps to repro:
1. Create a new Project.
2. Window > Asset Store.
3. Undock Asset Store window and dock it.
4. Repeat Step 3.

Actual Result:
Asset Store window gets blank and doesn't work.

Expected Result:
Asset Store window should show the proper UI every time.

Reproducible in:
2019.1.0a9, 2018.3.0b10, 2018.3.0b6, 2018.3.0b3.

Working Fine in:
2018.3.0b2, 2018.2.15f1.

Environment:
Linux & Windows 7